How to Reset a Tripped Safety Switch (RCD) and Find the Faulty Circuit
I had a young mum from Mitcham ring me on a wet Thursday afternoon a few months back. Her safety switch had tripped while she was warming the bub’s bottle in the microwave, and she’d been flicking it back up every 30 seconds for over an hour, getting more and more frantic as the lounge stayed dark and the fridge stayed off. By the time I got there, the rocker on the RCD was actually warm — you can damage a switch by repeatedly resetting it under load, and she’d come close. We isolated the fault in eight minutes flat: a 14-year-old beer fridge in the garage with a leaking compressor seal. Cost her $0 in callouts because I felt sorry for her and walked her through it on the phone next time. Cost her about $700 in a new fridge. Worth every cent. Here’s the appliance-by-appliance isolation method I use on call-outs, written out so you can do it yourself for free.
What you’ll need
- A torch (the switchboard cupboard is always the worst-lit cupboard in the house)
- A pen and notepad — old school, works
- Knowledge of which RCD covers which circuits (we’ll work this out in Step 2)
- About 20 minutes of patience — methodical wins this one
- Optional: a plug-in socket tester (covered in test a powerpoint with a $25 tester) for verifying outlets along the way
Step 1: Reset once and watch what happens
Open the switchboard. Find the RCD — it’s the bigger switch with a “T” or “TEST” button on the front. Push the switch firmly to OFF, then back to ON. Does it stay on? If yes, the trip was a momentary spike — lightning, a neighbour’s air-con starting, a globe blowing as it died. Note the time on your phone and move on. If it trips again immediately or within a few seconds, you’ve got a real fault. Continue.
Step 2: Map your RCD’s coverage
Modern Aussie boards usually have one RCBO per circuit (combined MCB + RCD) or one RCD covering multiple MCBs. Look at the labels. Common groupings: “RCD1: Power upstairs, Power downstairs” or “RCD1: All Power, RCD2: All Lights”. If unlabelled — and most pre-2000 Aussie boards aren’t — turn the RCD off and walk through the house with the torch. Anything still working is on a different RCD. Note which rooms and circuits are dead. AS/NZS 3000 has required RCD protection on socket and lighting circuits added since 1991, so the older the home, the patchier the coverage.
Step 3: Unplug everything on the affected RCD
Walk through every room covered by the dead RCD and unplug literally everything. Fridges, microwaves, phone chargers, lamps, fish tanks, the lot. If a powerpoint has a switch, turn that off too. Don’t forget the obvious culprits — washing machine, dishwasher, kettle, the toaster — and the not-so-obvious ones — the pool pump in the back shed, the bore pump in the laundry, the 4-way board behind the TV unit. I recieve calls weekly where the culprit turned out to be a forgotten phone charger plugged in behind a couch.
Step 4: Reset the RCD with everything unplugged
Push the RCD back to ON. Two outcomes:
- It holds: Good. The fault is in an appliance, not the wiring. Continue to Step 5.
- It trips: The fault is in the fixed wiring — a bathroom fan, a hardwired oven, a ceiling light, a degraded cable in a wet wall. That’s licensed work — call a sparky. Skip to Step 9.
Step 5: Plug appliances back in one at a time
Now the methodical bit. Plug in one appliance, turn it on, wait 30 seconds. Still on? Plug in the next. Write each one down as you go. The key is to wait long enough — a fridge compressor doesn’t kick in for a couple of minutes after plugging in, and a faulty fridge will only trip when the compressor starts. Same with chest freezers and old air-cons.
Step 6: Watch for the usual suspects first
Fifteen years of callouts, in order of frequency:
- Old fridges and chest freezers — worn motor windings leak current to earth. Anything pre-2010 is suspect.
- Pool pumps — the ones sitting outside have water-ingressed terminals. Davey, Onga, AstralPool — doesn’t matter, they all suffer eventually.
- Kettles and toasters — heating elements crack, water gets in. A $25 Kmart kettle can outlast a $300 Smeg if you’re unlucky.
- Bathroom heated towel rails — moisture intrusion at the cable gland.
- Garden lights and outdoor extensions — slug-eaten cable, water in the join, pegs through buried Cordtech.
- Cheap phone chargers — especially the unbranded $4 jobs from a service station.
Step 7: When the RCD trips, you’ve found it
Whichever appliance you plugged in last is the culprit. Unplug it. Reset the RCD. Plug everything else back in to confirm. The faulty appliance gets either thrown out, repaired, or in the case of a fridge or pool pump, taken to a service tech who can re-Megger it (test the insulation resistance properly).
Step 8: Test the RCD itself every quarter
While you’re at the switchboard, push the TEST button on the RCD. It should trip within 30 ms. If it doesn’t, the RCD itself is faulty and that IS a sparky job — about $150 to replace. AS/NZS 3760 actually requires you to test residential RCDs every six months; do it on the first of every quarter and you’ll never forget. Stick a sticker on the inside of the switchboard door with the test dates.
Step 9: The intermittent trip — the hardest fault
Two common causes I’ve chased to ground over the years. First: the fridge defrost cycle. Old fridges run a defrost heater every 6–8 hours that draws current through a thermostat. If that heater has degraded insulation, it’ll trip the RCD only when it cycles on — usually overnight. Solution: leave the fridge plugged in on its own circuit and note exactly when the RCD trips. Second: the hot water system. Aussie storage HWS heat overnight on off-peak tariff (Tariff 31/33 in NSW, controlled load in VIC). If the element has a slow leak to earth, the RCD trips when it switches on at 11pm. Both faults are diagnosable by the timing alone.
Step 10: Document what you found and learn from it
Write the appliance, date, and outcome in the switchboard cupboard with a Sharpie. “Aug 2026 — old beer fridge in garage tripped RCD2, replaced.” Next time something trips, you’ve got a maintenance log. Sounds anal. Saves you an hour next time and lets the next sparky who visits skip a heap of diagnostic time. Also worth photographing the labelled board so you have a copy if you ever sell. While you’re there, check your smoke alarms too — see how to test and replace smoke alarms.
When to call a tradie
Three scenarios where this method ends and a sparky’s begins. One: RCD trips with everything unplugged — that’s a fixed-wiring fault (a nail through a stud, a rodent chewing in the roof, degraded cable in a wet wall). Two: RCD won’t reset at all even with no load — faulty RCD or persistent earth fault. Three: the faulty appliance turns out to be hardwired (oven, cooktop, hot water system, ceiling fan, range hood) — that’s licensed work to repair or replace under AS/NZS 3000. Quote $150–$300 for fault-finding plus repair time. Worth it — chasing a wiring fault without a Megger and a thermal camera is like fishing without a rod.
Common screw-ups
- Repeatedly resetting an RCD that keeps tripping under load — you’ll damage the contacts and possibly the cable. Two tries, max, then isolate.
- Taping over the test button or replacing the RCD with a plain MCB to “stop the nuisance” — illegal, deadly, and voids your insurance after a fire.
- Skipping the wait time when plugging things back in — compressors and elements don’t kick in instantly, you’ll miss the real culprit.
- Assuming a storm-related trip is “just lightning” without re-testing afterwards — sometimes the surge has actually damaged an appliance.
- Calling out a sparky before doing Steps 3 and 4 — you’ll pay $180 for them to do exactly what you could have done in 20 minutes.
Cost & time
The whole DIY isolation takes 20 minutes if you’re methodical. A replacement RCD is $150 supplied and installed. A faulty appliance fix ranges from $0 (bin it) to a few hundred for a fridge service. If it turns out to be fixed wiring, budget $300–$600 for a sparky to find and fix the fault. Old-style single-RCD switchboards upgraded to per-circuit RCBOs cost $1,500–$3,500 and are well worth it on any home older than 2000.
Look, an RCD that keeps tripping is doing its job. Its telling you 30 mA of current is leaking somewhere it shouldn’t — almost always to earth via a degraded appliance. Don’t tape over the test button, don’t replace the RCD with a regular MCB, don’t ring an “electrician mate” who’ll bypass it. The 30 mA threshold is what stops the leak from becoming the lethal 100+ mA that stops your heart. Find the leaky appliance instead. Most of the time it’s a fridge over a decade old, and the universe is telling you it’s time. Here’s the safe play: methodical isolation, document what you find, replace what’s faulty, and use the test button quarterly.
